1. Field of the Invention
The present invention relates to an image forming apparatus and a method for controlling the same.
2. Description of the Related Art
Generally, in image forming apparatuses using an electrophotographic image forming process, the image density tends to fluctuate depending on various conditions, such as the usage environment and the number of pages printed. In particular, in color image forming apparatuses that perform color printing by superimposing toner images with a plurality of colors, fluctuations in the image density of various colors also causes fluctuations in the color balance (so-called tint).
Thus, in recent years, Japanese Patent Application Laid-open No. 11-65237 proposed a color image forming apparatuses in which the amount of toner of a test image that is formed on an image carrier or the like is detected, and the image density is controlled based on the detection results.
Image forming apparatuses have a plurality of image forming modes with respectively different processing speeds. Examples of these image forming modes include a normal speed mode for performing standard printing, and a lower speed mode. The lower speed mode is used when performing printing on an OHT (overhead transparency) sheet or on cardboard, at a speed lower than that of the normal speed mode.
Generally, when the image forming mode is changed, the image density characteristics also change. Accordingly, in order to obtain a good color balance in all image forming modes, it is necessary to perform image density control for all image forming modes.
However, if the image density control is performed for all of many image forming modes, then the time that is necessary for the image density control becomes very long. More specifically, the time during which an image cannot be formed (downtime) is increased, and thus it is not preferable. Moreover, consumables, such as toner, will be used up more than necessary.